The instant invention relates to image developing apparatus and specifically a developer roll for use in combination with a color producing substrate. In accordance with this invention, a color is formed by the reaction of isolated chromogenic materials. A first chromogenic material is typically a color precursor of the electron donating type whereas the second chromogenic material is typically identified as a color developer and is generally of the electron accepting type. In this invention a developer roll burnishes the active coating on the color producing substrate to promote the reaction of the color forming ingredients. This developing action is accomplished without "rupturing pressure" or without the necessity for pressure rollers which define a pressure nip.
One type of substrate for which image developing apparatus such as the developer roll of this invention is necessary is commonly referred to as carbonless paper. Carbonless paper is a common, commercially used type of pressure sensitve paper wherein during manufacture the backside of the paper substrate is coated with what is referred to as CB coating, the CB coating containing one or more color precursors generally in capsular form. At the same time the front side of the paper substrate is coated during manufacture with what is referred to as a CF coating, which contains one or more color developers. Both the color precursor and the color developer remain in the coating compositions on the respective back and front surfaces of the paper in colorless form.
This is true until the CB and CF coatings are brought into contiguous relationship and sufficient pressure, as by a typewriter or stylus, is applied to rupture the capsules in the CB coating to release the color precursor. At this time the color precursor contacts the CF coating and reacts with the color developer therein to form a color. Generally, this color is formed in a pattern of an image such as an alphanumeric character or the like. Thus the image from the top surface of the top sheet is transferred to the next sheet without the use of carbon paper.
A related product, and one for which the developer roll of this invention has special utility is referred to as self-contained paper. Very generally, self-contained paper refers to an image transfer system wherein only one side of the paper needs to be coated and the one coating contains both the color precursor, generally in encapsulated form, and the color developer. Thus, when pressure is applied, again as by a typewriter, stylus or other writing instruments, the color precursor capsule is ruptured and the internal phase reacts with the surrounding color developer to form an image. Both the carbonless paper system and the self-contained carbonless paper system have been the subject of a great deal of patent activity.
A second type of product which requires developer roll activity is described as self-developing film for use with fully automatic photographic cameras. Typical of these cameras and the film which is used in them is Polaroid Corporation's SX-70 and Pronto and Eastman Kodak Company's EK-6 and EK-8 cameras. These cameras and the film used therein are designed to automatically produce finished, waste free color prints with virtually no operator involved other than to compose the picture, focus and then actuate the camera by depressing its cycle start button.
Once actuated, the order of camera operations begins with exposure of a film unit. Afterwards, the exposed film unit is advanced from its exposure location into engagement with a film processing subsystem or apparatus which initiates a diffusion transfer process in the film unit while transporting it to the exterior of the camera where it becomes accessible to the photographer. After the diffusion transfer process is initiated, it develops and forms a visible image in the film unit in a well-known manner.
Typically necessary in systems such as this are pressure rollers to diffuse the active ingredients. See for example, U.S. Pat. No. 2,435,717 (1948) to Land; U.S. Pat. No. 2,495,113 (1950) to Gannon. Also described in the prior art are pressure ebbs for "film pods", see for example, U.S. Pat. No. 2,659,825 (1953) to Land or along the same lines squeezing rollers such as demonstrated by U.S. Pat. No. 2,751,814 (1956) to Limberger. Other patents generally known to be pertinent to this concept are U.S. Pat. No. 2,971,445 (1961) to Orlando; U.S. Pat. No. 3,134,313 (1964) to Gold et al.; U.S. Pat. No. 3,249,434 (1966) to Land et al.; U.S. Pat. No. 3,615,132 (1971) to Turner; U.S. Pat. No. 4,017,879 (1977) to Lermann et al.; U.S. Pat. No. 4,200,382 (1980) to Friedman; and U.S. Pat. No. 4,256,392 (1981) to Stemme et al.
Another line of products which typically require developer rolls or the like are described in previously mentioned U.S. Pat. No. 3,615,132 to Turner and assigned to the Xerox Corporation. These patents describe what is referred to as the process of xerography, which is also disclosed for example in Carlson Pat. No. 2,297,691. In this process a xerographic plate comprising a layer of photoconductive insulating material on a conductive backing is given a uniform electric charge over its surface and then exposed to the subject matter to be reproduced usually by conventional projection techniques. This exposure discharges the plate areas in accordance with the light intensity that reaches them, and thereby creates an electrostatic latent image on or in the photoconductive layer. Development of the latent image is effected with an electrostatically charged, finely divided material, such as an electroscopic powder, which is brought into surface contact with the photoconductive layer and is held thereon electrostatically in a xerographic powder image pattern corresponding to the electrostatic latent image. Thereafter, the developed xerographic powder image is usually transferred to a support surface, such as, a sheet of copy paper to which it may be fixed by any suitable means.
Since the disclosure in Carlson, many improvements have been in xerographic devices and techniques and, as a result, both manual and automatic machines for carrying out xerographic reproduction processes are in wide commercial use.
While a variety of commercial processes involving a color development or color transfer system have been described above, they all suffer from a common deficiency. In any of the systems wherein color development takes place between co-reactive materials, it is common to use pressure rollers for purposes of developing the color. This is done when the co-reactant materials are maintained in isolation from one another. By use of the apparatus and method of this invention pressure rollers are no longer necessary for the development of colors between co-reacted materials. Rather than use a pressure nip to crush, squeeze, diffuse or otherwise physically distort coatings or substrates a more subtle force is applied by means of the developer roll of this invention. The developer roll of this invention relies on a burnishing effect on the active surface of the reactive coating and the optional application of heat to develop, enhance and project developed colors. Common disadvantages of the high pressure rollers common to the prior art systems are that they require not only high pressure, but also precision alignment in order to develop color without crimping or creasing the sheet.
Several terms need to be defined for purposes of this application. The term "rupturing pressure" should be understood to mean the pressure necessary to crush microcapsules coated onto a paper substrate. In typical carbonles paper embodiments wherein rupturing pressure is applied by means of a typewriter or stytus-like instrument, in order to assure uniform capsule rupture a rupturing pressure of greater than 100 kg/cm.sup.2 is required.
The "force" necessary to release the internal phase of capsules shall be understood to mean the burnishing force, heat force or frictional force developed by use of the apparatus of this invention to rupture or release the contents of the microcapsules which have been coated onto the substrate.
The term "image-wise exposing" shall be understood to mean that the reaction between the chromogenic material and the developer occur according to the exposure such that a positive or negative image is obtained. The image may be formed by a change in color or a difference in contrast.